This invention relates to a method and apparatus for processing photographic material. In particular, the invention relates to a method of processing which uses a low volume of processing solution.
Conventional processing of photographic material requires the use of large tanks of processing solutions. Each tank contains a processing solution such as developer, bleach, fixing solution or washing solution. The material is transported through each tank in turn. There is a tendency for the solutions to carry over from one tank to another leading to pollution of the solutions. Conventional processing has several other drawbacks. The temperatures which can be utilized are limited and therefore the process is slow. The composition of the solutions must be stable over long time periods in the processing tanks. Replenishment of the solutions is difficult to control. The processing apparatus is also very large due to the number of processing tanks.
To overcome the problems of conventional deep tank processing surface application of the processing chemicals was developed. In previous surface application methods a volume of solution is applied to the surface of the material being processed. However, previous surface application methods have several drawbacks. If the solution applied to the material is just left on the material in a static condition the processing will be very slow and inefficient because there is no agitation and by-products accumulate in the material layers and slow down processing. This method is also prone to non-uniformity of processing.
It is also known to process the material within a rotary tube. The material to be processed is placed emulsion side facing inwards within the tube. Solution is added and the tube rotated. Large volumes of processing solution (70 ml/sq.ft and upwards) will process the material effectively so long as rotation is not so fast as to cause dispersion of the solution puddle. Rapid rotation of the device is however very desirable to quickly and evenly distribute a given small volume of solution over the whole surface of the material so that processing is uniform from one end to the other. If the rotation is too slow there will be seasoning of the small volume of solution by the front end of the material and processing will be different at the back end of the material. Small volumes of processing solution (50 ml/sq.ft or less) do not properly process film or paper because when the device is rotated, even at low speeds of rotation, the solution puddle is dispersed and spread over the whole surface of the material. Consequently there is no agitation. This leads to several processing defects. Processing is streaky, non-uniform and also slow because of local consumption and the accumulation of by-products. There is no surface mixing and chemical economy is therefore low.
Co-pending application no GB 0023091.2, filed on Sep. 20, 2000, discloses a single use wave processor and method of processing that employs volumes per linear foot of film that are similar to those used for replenishment of conventional deep tank processors. The wave processor uses these volumes and then disposes of them and therefore eliminates the need for standing tanks of solution. Processing solutions can be added directly to the processing chamber of the wave processor and a process cycle can consist of developer, stop, solution removal, bleach, solution removal, fix, solution removal and four wash stages with solution removal between stages. In this case solution removal is by vacuum suction of about 85% of the previous processing solution before the next one is added. This means a complete process is run in one processing vessel.
Processing solutions such as the developer can have a limited lifetime due to aerial oxidation and evaporation. In conventional processing machines in which developer-replenisher is used the developer-replenisher also has a limited lifetime. In Kodak SM processors the limited lifetime of these processing solutions has been overcome by using direct replenishment with concentrates. C-41 film developer has three concentrates which are metered into the developer tank at a rate proportional the amount of film processed. This maintains the developer solution at optimum composition.
In the case of the wave processor it is desirable to use similar concentrates to those used in the C-41 process. However, there is no developer solution and no bleach solution and no fixer solution in the processing vessel to add the concentrates to. The wave chamber is empty at the start of the process. In addition it is necessary to load the film into the processing space before the solutions are added. Adding concentrates directly on the film might cause processing uniformity problems. Furthermore it is desired to develop in about 30 seconds which leaves little time for mixing. If a film designed for the C-41 process which has a development time of 3 minutes 15 seconds is processed under more active conditions in 30 seconds it is found that the red and green contrasts are low compared to the blue contrast. These problems are overcome by the invention and additional benefits of the invention are also demonstrated.
It has been found that by adding a concentrate consisting of most of the components of the developer solution except the color developing agent directly to the film surface, leaving for a short time, then adding another concentrate consisting mainly of the color developing agent, that excellent photographic performance can be obtained. In comparison with a process in which a single pre-made developer solution, which is made from the same concentrates, is added to the film, a better photographic performance results from the two stage method.
According to the present invention there is provided a method of processing photographic material comprising the steps of applying a fixed volume of at least one of the processing solutions to the surface of the material such that the volume is spread and re-spread repeatedly over a given length of material in a rotating containment chamber, the fixed volume being applied in at least two stages, in the first stage the first volume is spread repeatedly by the formation of a standing wave of solution, in the second stage the second volume is added to the standing wave so as to mix coherently with the first volume, each stage lasts for a predetermined time period. Preferably the solution is agitated as it is applied to the surface of the material.
The photographic performance of two stage development is superior to that of the one stage development, for the same development time and the same chemical usage.
The method of the invention allows direct mixing of the component parts of a given processing solution in the processing chamber while the film is present.
The separated developer components used in two stage development are much more stable than the pre-mixed developer used in single stage development. Such components can therefore be stored for much longer time periods.
The method of the invention allows the material being processed to be wetted and partly swollen by the first or buffer stage of the process, before development starts. The buffer components of the developer are added first and it is thought that this allows the pH of the emulsion layers of the film to be closer the development pH before development starts compared with the case where development starts immediately. This is thought to be particularly true for the lowest or red emulsion layer.
The ratio of the two component parts of the two stage development process can be changed at will. Therefore the composition of the developer can be xe2x80x9cfine tunedxe2x80x9d for the particular material being processed. It is also possible to vary the relative treatment times of the first and second stages of the two stage development to allow xe2x80x9cfine tuningxe2x80x9d of the development to a particular film.